Instrument Description

CTD Unit and Auxiliary Sensors

Two CTD packages were used during RRS James Cook cruise 31 (JC031). The first CTD package (stations 1-12) comprised a Sea-Bird 911 plus CTD system, auxiliary sensors and Sea-Bird SBE 32, 24-way carousel fitted to a stainless steel frame with fin. During it's recovery at station 12 (08/02/2009), the package was pulled into the hydroboom block resulting in the total loss of the CTD package over the side. Consequently, the entire package was replaced (see below). A full description of the package is as follows:

The replacement CTD package (stations 13-84) also comprised a Sea-Bird 911 plus CTD system, auxiliary sensors and Sea-Bird SBE 32, 24-way carousel fitted to a stainless steel frame with fin. The LADCP (s/n 4275) was damaged during the deployment of station 35 and was replaced prior to station 36. A full description of this package is as follows:

BODC Processing

The data arrived at BODC in 81 Matlab (.MAT) format files. These represented all of the available measurements taken during the cruise that were processed using the shear method implemented in University of Hawaii software. The upcast and downcast data were reformatted into separate internal QXF format files using BODC transfer function 438. The following table shows how the downcast variables within the .MAT files were mapped to appropriate BODC parameter codes:

Originator's Variables

Units

Description

BODC Parameter Code

Units

Comment

d_samp

metres

Depth below sea surface (ADCP bin)

DBINAA01

metres

pxy

decimal degrees

latitude and longitude position at start

-

-

Not transferred

sm_dn_i

-

Flags indicating whether bin contains real or fill value (downcast)

-

-

Converted to BODC QC flags

sm_mn_i

-

Flags indicating whether bin contains real or fill value (mean)

-

-

Not converted - mean data are not transferred into QXF

sm_up_i

-

Flags indicating whether bin contains real or fill value (upcast)

-

-

Not converted

sn_dn_i

None

Number (per bin) of measurements by lowered acoustic doppler current profiler (ADCP) (downcast)

NLADCPBN

None

sn_mn_i

None

Number (per bin) of measurements by lowered acoustic doppler current profiler (ADCP) (mean)

-

-

Not transferred - mean data are not transferred into QXF

sn_up_i

None

Number (per bin) of measurements by lowered acoustic doppler current profiler (ADCP) (upcast)

-

-

Not transferred

su_dn_i

m s -1

Eastward current velocity (Eulerian) in the water column (downcast)

LCEWLW01

cm s -1

Velocity * 100

su_mn_i

m s -1

Eastward current velocity (Eulerian) in the water column (mean)

-

-

Not transferred - can be derived from upcast and downcast velocities

su_up_i

m s -1

Eastward current velocity (Eulerian) in the water column (upcast)

-

-

Not transferred

sv_dn_i

m s -1

Northward current velocity (Eulerian) in the water column (downcast)

LCNSLW01

cm s -1

Velocity * 100

sv_mn_i

m s -1

Northward current velocity (Eulerian) in the water column (mean)

-

-

Not transferred - can be derived from upcast and downcast velocities

sv_up_i

m s -1

Northward current velocity (Eulerian) in the water column (upcast)

-

-

Not transferred

sw_dn_i

m s -1

Upward current velocity in the water column (downcast)

LRZALW01

cm s -1

Velocity * 100

sw_mn_i

m s -1

Upward current velocity in the water column (mean)

-

-

Not transferred - can be derived from upcast and downcast velocities

sw_up_i

m s -1

Upward current velocity in the water column (upcast)

-

-

Not transferred

sv_var_dn_i

m s -1

Variance of shear in the northward velocity component (downcast)

SDNSLW01

cm s -1

(variance 0.5 ) * 100

sv_var_mn_i

m s -1

Variance of shear in the northward velocity component (mean)

-

-

Not transferred - can be derived from upcast and downcast velocities

sv_var_up_i

m s -1

Variance of shear in the northward velocity component (upcast)

-

-

Not transferred

sw_var_dn_i

m s -1

Variance of shear in the upward velocity component (downcast)

SDZALW01

cm s -1

(variance 0.5 ) * 100

sw_var_mn_i

m s -1

Variance of shear in the upward velocity component (mean)

-

-

Not transferred - can be derived from upcast and downcast velocities

sw_var_up_i

m s -1

Variance of shear in the upward velocity component (upcast)

-

-

Not transferred

su_var_dn_i

m s -1

Variance of shear in the eastward velocity component (downcast)

SDEWLW01

cm s -1

(variance 0.5 ) * 100

su_var_mn_i

m s -1

Variance of shear in the eastward velocity component (mean)

-

-

Not transferred - can be derived from upcast and downcast velocities

su_var_up_i

m s -1

Variance of shear in the eastward velocity component (upcast)

-

-

Not transferred

txy_start_end

decimal

Day, latitude and longitude at start and end of profile

-

-

Not transferred into QXF

The reformatted data were visualised using the in-house EDSERPLO software. Suspect data were marked by adding an appropriate quality control flag, missing data by both setting the data to an appropriate value and setting the quality control flag.

Originator's Data Processing

Sampling Strategy

The aim of JC031 was to occupy repeats of hydrographic sections in Drake Passage. The sections studied are as follows: Section SR1 (also known as A21), which is located in Drake Passage between the Southern tip of South America and the West Antarctic Peninsula; section SR1b is located further to the east. In addition to the previous section of SR1b, extra stations were sampled on the northern side of the Burdwood Bank, located south of the Falkland Islands. The data collected during JC031 comprised physical, chemical and biological measurements. There were five main scientific teams, physics, nutrients and oxygen, carbon, CFC's and transient tracers, and biology (phytoplankton). The data will contribute to the current knowledge of the physical, chemical and biological properties in this region, and will also allow comparisons to be drawn with previous cruise data so that the change in water properties and transport through Drake Passage from west to east can be observed.

In total 84 CTD (conductivity-temperature-depth) stations were occupied. A 24-bottle rosette was used to take water samples at these CTD stations. Also mounted on the frame was a LADCP (lowered acoustic doppler current profiler), fluorometer, transmissometer, and a dissolved oxygen sensor. Of these casts, only 81 yielded LADCP measurements. This was due to an incident with the winch during station 12 which caused the total loss of the CTD package (including LADCP). Data was not collected during station 13 as this was only a test station. Station 50 did not yield any LADCP data because the deploy command was not sent. Stations 35 and 36 were repeats of station 34.

Data Processing

Data collected from the instrument was downloaded after each cast by the technician on watch. Subsequently, data were processed using two methods; the shear method implemented in University of Hawaii software and the least squares method implemented in LDEO software version 7. Further information about processing methods can be found in the report (from p68) for cruise RRS Charles Darwin 139 (CD139). Additional information can also be found in the LADCP report from cruise JC031.

The Natural Environment Research Council (NERC) funds the Oceans 2025 programme, which was originally planned in the context of NERC's 2002-2007 strategy and later realigned to NERC's subsequent strategy (Next Generation Science for Planet Earth; NERC 2007).

Who is involved in the programme?

The Oceans 2025 programme was designed by and is to be implemented through seven leading UK marine centres. The marine centres work together in coordination and are also supported by cooperation and input from government bodies, universities and other partners. The seven marine centres are:

National Oceanography Centre, Southampton (NOCS)

Plymouth Marine Laboratory (PML)

Marine Biological Association (MBA)

Sir Alister Hardy Foundation for Marine Science (SAHFOS)

Proudman Oceanographic Laboratory (POL)

Scottish Association for Marine Science (SAMS)

Sea Mammal Research Unit (SMRU)

Oceans2025 provides funding to three national marine facilities, which provide services to the wider UK marine community, in addition to the Oceans 2025 community. These facilities are:

British Oceanographic Data Centre (BODC), hosted at POL

Permanent Service for Mean Sea Level (PSMSL), hosted at POL

Culture Collection of Algae and Protozoa (CCAP), hosted at SAMS

The NERC-run Strategic Ocean Funding Initiative (SOFI) provides additional support to the programme by funding additional research projects and studentships that closely complement the Oceans 2025 programme, primarily through universities.

What is the programme about?

Oceans 2025 sets out to address some key challenges that face the UK as a result of a changing marine environment. The research funded through the programme sets out to increase understanding of the size, nature and impacts of these changes, with the aim to:

improve knowledge of how the seas behave, not just now but in the future;

help assess what that might mean for the Earth system and for society;

assist in developing sustainable solutions for the management of marine resources for future generations;

enhance the research capabilities and facilities available for UK marine science.

In order to address these aims there are nine science themes supported by the Oceans 2025 programme:

Climate, circulation and sea level (Theme 1)

Marine biogeochemical cycles (Theme 2)

Shelf and coastal processes (Theme 3)

Biodiversity and ecosystem functioning (Theme 4)

Continental margins and deep ocean (Theme 5)

Sustainable marine resources (Theme 6)

Technology development (Theme 8)

Next generation ocean prediction (Theme 9)

Integration of sustained observations in the marine environment (Theme 10)

In the original programme proposal there was a theme on health and human impacts (Theme 7). The elements of this Theme have subsequently been included in Themes 3 and 9.

When is the programme active?

The programme started in April 2007 with funding for 5 years.

Brief summary of the programme fieldwork/data

Programme fieldwork and data collection are to be achieved through:

physical, biological and chemical parameters sampling throughout the North and South Atlantic during collaborative research cruises aboard NERC's research vessels RRS Discovery, RRS James Cook and RRS James Clark Ross;

the Continuous Plankton Recorder being deployed by SAHFOS in the North Atlantic and North Pacific on 'ships of opportunity';

physical parameters measured and relayed in near real-time by fixed moorings and ARGO floats;

The data is to be fed into models for validation and future projections. Greater detail can be found in the Theme documents.

Oceans 2025 Theme 1: Climate, Ocean Circulation and Sea Level

Through fieldwork, analysis and modelling, Theme 1 will provide detailed knowledge of how the Atlantic, Arctic and Southern Oceans are responding to, and driving, climate change. In combination with geodetic studies, it will also improve our ability to predict global sea level and UK land movements in the century ahead.

The official Oceans 2025 documentation for this Theme is available from the following link: Oceans 2025 Theme 1

This Work Package is run by the National Oceanography Centre, Southampton (NOCS) and aims to establish regional budgets of heat, freshwater and carbon, and to develop more accurate parameterisations for predictive ocean models by quantitatively investigating diapycnal and isopycnal transport processes using observations.

Vast, though poorly quantified, amounts of anthropogenic CO2 (~20 Pg) are believed to have been absorbed into the Antarctic mode and intermediate waters. Much of this uptake is achieved in the Antarctic Circumpolar Current (ACC), involving the upwelling of North Atlantic Deep Water, its northward transport by a delicate balance between Ekman drift and eddies, followed by subduction as mode waters. Models suggest that the rate of CO2 uptake is sensitive to changes in the wind and to changes to the eddy fluxes (Mignone et al., 2005).

To predict climate change, it is essential that the size of this carbon sink be known, and the processes that control it be understood. Even the exchanges of heat and freshwater between the Atlantic and Southern Oceans are poorly known. NOCS will combine observations and modelling to quantify and understand the processes controlling property fluxes and trends in the Atlantic sector of the Southern Ocean, where the Atlantic overturning circulation is partially closed as it meets the ACC. The observational effort will be fully integrated with the international Climate Variability and Predictability (CLIVAR)/Carbon repeat hydrography program, and with the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) initiative to study mixing rates and processes; this work has been accepted as a contribution to the International Polar Year. The budgets and mixing rates inferred from field measurements will be used to both evaluate and improve numerical models.

More detailed information on this Work Package is available at pages 10 - 11 of the official Oceans 2025 Theme 1 document: Oceans 2025 Theme 1

Fixed Station Information

WOCE established a repeat hydrographic section across Drake Passage and designated it SR1 (also known as A21). The section is located between the Southern tip of South America and the West Antarctic Peninsula within a bounding box of 55° 19.40' S, 68° 15.80' W (North-Western corner) and 64° 8.52' S, 63° 4.80' W (South-Eastern corner).

A table of cruises which occupied SR1 is presented below with links to the relevant cruise reports (where available).

Fixed Station Information

Station Name

Drake Passage

Category

Offshore area

Latitude

59° 0.00' S

Longitude

62° 0.00' W

Water depth below MSL

Drake Passage

The World Ocean Circulation Experiment (WOCE, 1990-1998) was a major international experiment which made measurements and undertook modelling studies of the deep oceans in order to provide a much improved understanding of the role of ocean circulation in changing and ameliorating the Earth's climate.

The Drake Passage is the narrowest constriction of the Antarctic Circumpolar Current (ACC) - the largest current in the world and connects all three major oceanic basins both horizontally and vertically, thus being a key control in the global overturning circulation.Within the Drake Passage, two repeat hydrographic sections (SR1 and SR1b) were established by WOCE. These were designed to extend measurements collected earlier by the International Southern Ocean Studies (ISOS) programme and have continued beyond the WOCE time-frame.

The original section was SR1 (which also covers part of the A21 one time survey track). Subsequently, the section was shifted to the east (and designated SR1b) in order for it to lie on a satellite ground track as illustrated in the image below.

In addition to the hydrographic measurements, UK research in Drake Passage also includes a network of coastal and deep tide gauges, analysis of satellite altimeter data, and state-of-the-art global numerical modeling.